Arrangement for producing filters



March 28, 1944. M, VON ARDENNE ARRANGEMENT FOR PRODUCING FILTERS FiledMarch 24, 1941 4ft orney,

Patented Mar. 28, 1944 ARRANGEMENT FOR PRODUCING FILTERS Manfred vonArdenne, Berlin-Hcliteflelde, Gelmany; vested in the Alien PropertyCustodian/ '5 Application March 24, 1941, Serial No. 385,034 3 v InGermany February 19, 1940 v ,j

7 Claims.

This invention relates to an arrangement for producing filters.

To produce surface filters and ultra-filters which have the propertiesof an ideal filter it is known in the art to burn in a foil with the aidof ion rays perforations of constant magnitude and form and in a desiredspaced relation from one another.

The object of the present invention is to provide an arrangement,whereby the greatest possible number of very fine perforations are burntin a filter film so as to reduce the filter resistance (resistance toflow). This may be accomplished according to the invention by the factthat the cross-section through which pass the ion rays issuing from theion emitting source is projected by means of an electrostatic multiplelens on the foil to be perforated. To this end, a short focus multiplelens is preferably employed in front of the foil. By providing theelectrostatic multiple lens with a plurality of accurately alignedperforations, it is also possible to burn when producing filters acorresponding plurality of perforations in the foil. In carrying theinvention into practice a multiple lens is preferably employedconsisting of two electrodes impressed with a high negative potentialand provided with a plurality of perforations and of an electrodeinterposed between these two electrodes and impressed with a lowernegative potential and also provided with perforations.

Since the distance between the individual elements of the multiple lensis relatively great, perforations are obtained in the foil during thebuming operation between which there may be relatively broad stripes ofthe foil which are not perforated. In order to provide also thesestripes with perforations to the greatest possible extent, thearrangement according to the invention is so designed that the ion raysmay be deflected after the first burning operation by means ofdeflecting magnetic fields in a corresponding manner.

A further possibility of increasing the number of perforationsobtainable with one burning operation consists according to theinvention in the fact that the ion emitting source is provided in aknown manner with two electrodes having a plurality of perforationswhich form a plurality of cross-sections for the passage of electronrays. By means of the multiple lens not only a single ion raycross-section but a plurality of ion ray crosssections are thereforeprojected simultaneously.

In the accompanying drawing, Fig. 1, is shown an embodiment of theinvention in diagrammatic form. The reference numeral i denotes a canalray tube in which is arran'gedfanfloidde-coated incandescent cathode 2.1Directly infront of the incandescent cathodearetwoseries-arrangedelectrodes. canal." Theselielectrodes are each provided with apluralijtyiof accuratel aligned perforationst and 6;,'respectively.'These electrodes are spaced frpmjeachother adistance of about 3 mm..;Thelelec't'rode 3j may, for instance, be impressed'witlila voltageof+40. volts and the electrode 4 with a voltagegof 520,000 volts. Hydrogenat a pressure 'oflifi' millimeters Hg may be supplied to thfe tubeq' The,arclgas discharge resulting therefrom may, for instance, burn at apotential of 40 volts; Injthis known arrangement an ion emitting sourceis providedby means of which a plurality of fine; ion rayso'rrespondingto the numberlof perforationsj and 6 is produced. The'referencehuiiierals 8, 9 denote an electrostatic short .focus multiplelens which serves to projectthe numerous cross-sections for the passageof theion rays" on a foil l4 arranged directly behind the multiple lens.To this end, the foil It is, stretched onacar'rier ii. The threeelectrodes of the multiple lens areeach provided with a plurality ofperforations 10,1 and 12. In this manner a numberofelements of themultiple lens are obtained icorresponding to the number of theperforations. The central electrode l is, for instance, impressed with apotential of 5,000 volts, whereas the other two electrodes 8 and 9 witha potential of 20,000 volts.

In the operation of the device a plurality of fine ion rays are emittedat the openings 6 of electrode 4, as previously mentioned. These raysare so formed, due to the potential on the electrode 4. that each rayhas a sufficiently large cross-section in the plane of the electrostaticmultiple lens 1-9 to cover the entire area of the lens. Thus the ionscomposing small sections of each ray enter the openings H of the frontelectrode 8 of the multiple lens 1-9. Looking at it from the standpointof the multiple lens, each individual lens thereof receives a pluralityof ion ray sections, which are parts of the ion rays emitted from theplurality of openings 6, respectively. The ray sections received by eachindividual lens are affected by the lens potential in known manner andare focused on the foil l4, whereby perforations are burned in the foil.In this connection, it may be pointed out that since each ray sectionreceived at an individual lens reaches the lens from a differentdirection from the directions of the other ray sections, these raysections are focused at different points on the foil l4, and theperforaticn pattern producedat the foil is a reproduction oi the openingpattern at electrode 4, although much reduced in size.

In llig. 2 is shown a top view of a portion of the foil film it providedwith perforations obtained by the burning process. The referencenumerals l1, l8, l9 and I denote fields of filter perforations, eachproduced by one element of the multiple lens. Each perforation in such afield corresponds to the projection of a corresponding perforation inthe electrodes 3 and 4 of the electron emitting source as aboveexplained.

Since from a constructional point of view the distance a between theindividual fields of the perforations produced by each element of themultiple lens is great in proportion to the width b or the field, alsothe portions of the foil not yet provided with perforations may beperforated by the use of electrostatic deflecting fields which may be,for instance, produced by deflecting plates is and it which deflect theion rays in a known manner. With the aid of the above-describedarrangement the greatest possible number of fine, nay ultra-microscopicfilter perforations may be attained. Assuming, for instance, that in theelectrode 4 there are one hundred perforations of a diameter of 0.5 mm.and that the electrostatic multiple lens has 50 perforations, 5,000periorations are obtained at the same time in the filter foil with oneburning operation.

When carrying the invention into practice it is particularlyadvantageous to use such ions which react with the filter substance.This is, for instance, the case when employing oxygen and pyroxylinfoils.

What is claimed is:

1. An arrangement for producing filters, where'- by fine perforationsare made in a foil by means of ion rays, comprising a source of ions, anelectrostatic multiple lens for forming a plurality of overlappin ionbeams, and a second electrostatic multiple lens arranged to produce aplurality of ion beams from each of said first mentioned beams andproject them on the foil to be perforated.

' 2. An arrangement for producing filters, whereby fine perforations aremade in a foil by means of ion rays. comprising a multiple electrostaticlens for projecting ions on to the foil to be perforated, a source ofions, and a second multiple electrostatic lens for directing a pluralityof beams of ions toward said first multiple lens, the firstmentioned ofsaid multiple electrostatic lenses receiving in each of its individuallenses a part of each of said beams of ions whereby each of saidindividual lenses directs a pattern of individual beams composed ofindividual parts or each of said beams.

3. An arrangement as set forth in claim 1, wherein the projecting lenscomprises three spaced electrodes having aligned perforations therein,the two outer electrodes being impressed with a high negative potentialand the central electrode with a lower negative potential.

ad/Anarrangelhent according to claim 1, where in the ionsiare producedfrom a gas whichis capable of reacting with the toil.

5. Apparatus for producing fine perforations in a foil or the like,comprising a source of ions, means cooperating with said source to forma plurality of ion rays which have overlapping cross-sections in a givenplane, and a multiple lens located substantially in said plane, saidlens comprising a plurality of individual lenses each operative toreceive a section of each oi said ion rays and focus such sections atdifferent points, respectively, on said foil.

6. In apparatus for producing filters by making perforations in a foilby means of ion rays, means constituting a source of a plurality ofindividual beams having overlapping cross-sections with the central axisof all of the beams substantially parallel but with the rays formingeach beam out of parallel relationship, and a multiple lens assemblypositioned in the path of said beams comprising a plurality ofindividual lenses each of which is operative to receive a section ofeach of said beams and direct the sections at diiferent pointsrespectively on the foil.

7. Apparatus as described in claim: 6 wherein deflectors are provided atthe sides of the path of the beams for producing a field to defiect thebeams.

MANFRED VON ARDENNE.

